For me, what I did was spray a bunch in one area, letting it pile up slightly...move to a new area and repeat. I didnt like doing back forth across like that because it started to look real un-natural. Once the first layer has cured (overnight) I then, very gently, sprayed a little with the can raised off the egg crate...this will give you "stringy" foam that I randomly placed, dragged and dabbed all over the other larger created pieces of foam. You really have to play with it to get it at the point where your happy with it. After the foam has cured, once again over night, if you want to modify the look, I found the best way is to just tair chuncks of foam away (to make holes, caves, pass thrus etc). I tried using a straight edge and found it was'nt as effective as using your hand. When you tair it away with your hand, you will see that it will come kind off in layers.
As for the epoxy, I just waited overnight until to foam was cured. The epoxy is a big pain in the *** in my opinion. I used a 2 part boat hobby epoxy...it says 45 min cure time, but on the back of the bottle at the bottom it states, in fine print of course, that if both bottles are mixed 100% of its contents at once, it starts to cure it 10 minytes not 45!!! The second batch of epoxy I tried using half the bottles together...not so good because your paint brush will start to harden in about 10-15 minutes, so you either have to have a second brush or just do it all quickly. Once the epxoy is spread out over the foam, then you can sprinkle crushed coral or sand on it. Just thought I'd give you a heads up using the epoxy...WORK QUICKLY!!!
It would be great if someone could come up with a reef safe spray type of bonding agent. It would make life a whole lot easier, but until then we have to work with what we got.
Hope this helps, and good luck.